1. Field of the Invention
The present invention relates to a developing device for use in electrophotographic machines and the like, and more specifically relates to a monocomponent type developing device using only a toner as the developing material.
2. Description of the Related Arts
Conventional monocomponent type developing devices using only a toner as the developing material typically supply a nonmagnetic toner to the surface of an elastic roller for transporting said toner, and charge the aforesaid toner supplied to the surface of the elastic roller through pressure applied by a blade or similar type of toner regulating member which also regulates the thickness of the toner layer on the surface of the elastic roller.
The surface of the elastic roller, upon which is formed a toner layer of a specified thickness as previously described, makes touching contact with the surface of an image bearing member such as a photoconductive drum or the like, so as to transfer the toner from the aforesaid elastic roller to the specified location of an electrostatic latent image formed on the surface of the aforesaid image bearing member.
In the aforesaid type of developing device, the surface hardness of the elastic roller must be relatively high because the toner supplied to the surface of the elastic roller is electrically charged through pressure contact with a blade or similar toner regulating member.
Further, in the process wherein the surface of the elastic roller makes contact with the surface of the image bearing member to supply toner to the location of the electrostatic latent image formed on the surface of said image bearing member, the entire surface of said elastic roller along the axial direction must lightly come into contact with the surface of the image bearing member because the surface of said image bearing member may be damaged and the image formed on the image bearing member may be disturbed through contact with the elastic roller.
However, it is extremely difficult to accomplish the previously described light contact between the entire surface along the axial direction of the elastic roller having a relatively high hardness and the surface of the image bearing member. Therefore, one or the other of the aforesaid requirements must be sacrificed in the previously mentioned types of conventional developing devices, causing certain disadvantages which lead to inadequate image quality.
A developing device having the construction shown in FIG. 1 has been proposed to eliminate the disadvantages of previously described monocomponent type developing device. As shown in FIG. 1, a pliable sleeve-like toner transporting member 2 having a diameter greater than drive roller 1 is disposed around the exterior circumference of said drive roller 1, and a guide member 3, which is formed in a semicircular shape with an interior diameter that is the same as the exterior diameter of drive roller 1, is provided in the axial direction on both sides of said toner transporting member 2, such that toner transporting member 2 makes pressure contact with drive roller 1 by means of said guide member 3 excluding the developing region wherein member 2 confronts the surface of photoconductive member 4. At the same time, member 2 forms a slack portion "D" that protrudes from drive roller 1 in the developing region wherein member 2 confronts photoconductive member 4, such that said slack portion "D" makes light contact with the surface of photoconductive member 4.
In the case of the aforesaid developing device, drive roller 1 is rotated in the arrow "a" direction by a driving device such as a motor or the like (not shown in the drawing), and toner transporting member 2 which is pressed against drive roller 1 by means of guide member 3 is driven by means of the frictional force produced between said toner transporting member 2 and drive roller 1.
While toner 5 is in transit being transported to the photoconductive member 4 side by toner transporting member 2 driven in the previously described manner, the quantity of toner supplied onto the toner transporting member 2 is regulated by regulating blade 8, and after toner 5 is sufficiently triboelectrically charged between regulating blade 8 and toner transporting member 2 the slack portion "D" of toner transporting member 2 makes light contact with the surface of photoconductive member 4 in the developing region as previously described so as to transfer the triboelectrically charged toner 5 supplied from toner transporting member 2 to the surface of photoconductive member 4.
When the previously described developing device is used, toner 5 can be adequately charged, and toner 5 can be supplied to the location of the electrostatic latent image formed on the surface of photoconductive member 4 without damaging the surface of said photoconductive member 4.
In the aforesaid developing device, toner transporting member 2 is pressed against drive roller 1 by guide member 3, and toner transporting member 2 is driven in conjunction with the rotation of drive roller 1 by means of the frictional force produced between drive roller 1 and toner transporting member 2 by the force of the aforesaid pressure contact therebetween. Accordingly, toner transporting member 2 must be uniformly pressed agaist drive roller 1 with a constant pressure by guide member 3 to achieve suitable stable driving rotation of said toner transporting member 2.
When the aforesaid guide member 3 is formed of a polyacetal, phenol, nylon or like resin, a high degree of precision is required when setting the guide member to the device and manufacturing of guide member 3 in order to achieve suitable stable driving rotation of toner transporting member 2 in conjunction with the rotation of drive roller 1, thereby causing an extremely difficult problem in the manufacture of said guide member 3.
Further, when disturbances occur during the formation of guide member 3 with the resin and the internal diameter of guide member 3 becomes larger, toner transporting member 2 cannot be smoothly and uniformly pressed against drive roller 1 by guide member 3, causing toner transporting member 2 to slip. This slip causes toner 5 to be unstably transported by toner transporting member 2 and produces irregularities in the density of the image. On the other hand, when the internal diameter of guide member 3 becomes smaller, a large torque is required to drive the rotation of drive roller 1, thereby causing damage to toner transporting member 2.
The aforesaid guide member 3 may also be formed of pliable expanded material such as molto pren (Trademark) and the like. However, when toner transporting member 2 is pressed against drive roller 1 by a guide member 3 made of the aforesaid expanded material, it is difficult to press toner transporting member 2 against drive roller 1 with stable pressure, such that the state of contact of toner transporting member 2 with the surface of photoconductive member 4 is nonuniform, thereby producing the problem of irregular image density. After long-term use, the expanded material becomes fatigued, thereby reducing the pressure contact force applied by guide member 3 and causing the toner transporting member to slip.